A resurgence in the popularity of traditional swaddling has prompted fears of a rise in developmental hip problems in babies, which are now known to be linked to the technique, warns a paediatric orthopaedic surgeon in the Archives of Disease in Childhood.
The swaddling of infants used to be an almost universal practice, but fell out of favour in many parts of the world.
But the technique, which involves the binding or bundling of babies in blankets with their arms restrained and the legs stretched out, has recently become fashionable again, because of its perceived calming effects, says Professor Nicholas Clarke, of Southampton University Hospital.
Nine out of 10 infants in North America are now swaddled in the first six months of life, and demand for swaddling clothes soared by 61% in the UK between 2010 and 2011.
The evidence suggests that swaddling helps induce sleep and soothes excessive crying and colic. But there is also a growing body of evidence to show that it is linked to a heightened risk of developmental hip abnormalities.
This is because it forces the hips to straighten and shift forward, risking the potential for misalignment, and this in turn is associated with an increased risk of osteoarthritis and hip replacement in middle age.
In Japan an educational programme to encourage grandmothers not to swaddle their grandchildren prompted the prevalence of hip dislocation to halve.
Around one in five babies is born with a hip abnormality, with factors such as a breech birth or a family history, recognised risk factors. But mechanical factors after birth also have a role, says Professor Clarke. While many of these cases resolve spontaneously, swaddling may delay this.
Professor Clarke advises that swaddling can be safe provided that it doesn't prevent the baby's legs from bending up and out at the hips, because this position allows for natural development of the hip joints. The babies' legs must not be tightly wrapped and pressed together, he warns.
Any commercial swaddling products should include a loose pouch or sack for the babies' legs and feet, allowing for plenty of hip movement, he says.
Healthcare professionals need to do their bit by giving mums the correct advice about how to swaddle their child safely, to ward off hip abnormalities and other potential problems in later life, he says.
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